SVOboy: You should try using a polyurethane based glue. An expensive example is Gorilla glue. They make a "geneic" that's available at Home Depot, that work's just as well, as far as I can tell. The glue "set's up" from a chemical reaction with the humidity. It expands a little bit when it's setting up, but once it's stuck, it is flexible, but it won't come off. I have a piece of wood I glued to a cinder block fence about 10 years ago and the board is still there, even though the gate bang's on it every time someone goes in and out of the front yard. Be wise and use rubber glove's, though, it does not wash off and it takes day's for it to wear off.
I would be more worried about the electronics getting cooked by the high temperatures - wrecked some Nicad cells in my GPS on the dask of the car - and the ScanGaugeI + II should be kept cooler than 160F or else they can start drawing more power when off and fry. Not good having a car fire on the plastic dash!